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Next: <a href="Data-Output.html#Data-Output" accesskey="n" rel="next">Data Output</a>, Up: <a href="Assembler-Format.html#Assembler-Format" accesskey="u" rel="up">Assembler Format</a> &nbsp; [<a href="index.html#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="Option-Index.html#Option-Index" title="Index" rel="index">Index</a>]</p>
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<hr>
<a name="The-Overall-Framework-of-an-Assembler-File"></a>
<h4 class="subsection">18.20.1 The Overall Framework of an Assembler File</h4>
<a name="index-assembler-format"></a>
<a name="index-output-of-assembler-code"></a>

<p>This describes the overall framework of an assembly file.
</p>
<a name="index-default_005ffile_005fstart"></a>
<dl>
<dt><a name="index-TARGET_005fASM_005fFILE_005fSTART"></a>Target Hook: <em>void</em> <strong>TARGET_ASM_FILE_START</strong> <em>(void)</em></dt>
<dd><p>Output to <code>asm_out_file</code> any text which the assembler expects to
find at the beginning of a file.  The default behavior is controlled
by two flags, documented below.  Unless your target&rsquo;s assembler is
quite unusual, if you override the default, you should call
<code>default_file_start</code> at some point in your target hook.  This
lets other target files rely on these variables.
</p></dd></dl>

<dl>
<dt><a name="index-TARGET_005fASM_005fFILE_005fSTART_005fAPP_005fOFF"></a>Target Hook: <em>bool</em> <strong>TARGET_ASM_FILE_START_APP_OFF</strong></dt>
<dd><p>If this flag is true, the text of the macro <code>ASM_APP_OFF</code> will be
printed as the very first line in the assembly file, unless
<samp>-fverbose-asm</samp> is in effect.  (If that macro has been defined
to the empty string, this variable has no effect.)  With the normal
definition of <code>ASM_APP_OFF</code>, the effect is to notify the GNU
assembler that it need not bother stripping comments or extra
whitespace from its input.  This allows it to work a bit faster.
</p>
<p>The default is false.  You should not set it to true unless you have
verified that your port does not generate any extra whitespace or
comments that will cause GAS to issue errors in NO_APP mode.
</p></dd></dl>

<dl>
<dt><a name="index-TARGET_005fASM_005fFILE_005fSTART_005fFILE_005fDIRECTIVE"></a>Target Hook: <em>bool</em> <strong>TARGET_ASM_FILE_START_FILE_DIRECTIVE</strong></dt>
<dd><p>If this flag is true, <code>output_file_directive</code> will be called
for the primary source file, immediately after printing
<code>ASM_APP_OFF</code> (if that is enabled).  Most ELF assemblers expect
this to be done.  The default is false.
</p></dd></dl>

<dl>
<dt><a name="index-TARGET_005fASM_005fFILE_005fEND"></a>Target Hook: <em>void</em> <strong>TARGET_ASM_FILE_END</strong> <em>(void)</em></dt>
<dd><p>Output to <code>asm_out_file</code> any text which the assembler expects
to find at the end of a file.  The default is to output nothing.
</p></dd></dl>

<dl>
<dt><a name="index-file_005fend_005findicate_005fexec_005fstack"></a>Function: <em>void</em> <strong>file_end_indicate_exec_stack</strong> <em>()</em></dt>
<dd><p>Some systems use a common convention, the &lsquo;<samp>.note.GNU-stack</samp>&rsquo;
special section, to indicate whether or not an object file relies on
the stack being executable.  If your system uses this convention, you
should define <code>TARGET_ASM_FILE_END</code> to this function.  If you
need to do other things in that hook, have your hook function call
this function.
</p></dd></dl>

<dl>
<dt><a name="index-TARGET_005fASM_005fLTO_005fSTART"></a>Target Hook: <em>void</em> <strong>TARGET_ASM_LTO_START</strong> <em>(void)</em></dt>
<dd><p>Output to <code>asm_out_file</code> any text which the assembler expects
to find at the start of an LTO section.  The default is to output
nothing.
</p></dd></dl>

<dl>
<dt><a name="index-TARGET_005fASM_005fLTO_005fEND"></a>Target Hook: <em>void</em> <strong>TARGET_ASM_LTO_END</strong> <em>(void)</em></dt>
<dd><p>Output to <code>asm_out_file</code> any text which the assembler expects
to find at the end of an LTO section.  The default is to output
nothing.
</p></dd></dl>

<dl>
<dt><a name="index-TARGET_005fASM_005fCODE_005fEND"></a>Target Hook: <em>void</em> <strong>TARGET_ASM_CODE_END</strong> <em>(void)</em></dt>
<dd><p>Output to <code>asm_out_file</code> any text which is needed before emitting
unwind info and debug info at the end of a file.  Some targets emit
here PIC setup thunks that cannot be emitted at the end of file,
because they couldn&rsquo;t have unwind info then.  The default is to output
nothing.
</p></dd></dl>

<dl>
<dt><a name="index-ASM_005fCOMMENT_005fSTART"></a>Macro: <strong>ASM_COMMENT_START</strong></dt>
<dd><p>A C string constant describing how to begin a comment in the target
assembler language.  The compiler assumes that the comment will end at
the end of the line.
</p></dd></dl>

<dl>
<dt><a name="index-ASM_005fAPP_005fON"></a>Macro: <strong>ASM_APP_ON</strong></dt>
<dd><p>A C string constant for text to be output before each <code>asm</code>
statement or group of consecutive ones.  Normally this is
<code>&quot;#APP&quot;</code>, which is a comment that has no effect on most
assemblers but tells the GNU assembler that it must check the lines
that follow for all valid assembler constructs.
</p></dd></dl>

<dl>
<dt><a name="index-ASM_005fAPP_005fOFF"></a>Macro: <strong>ASM_APP_OFF</strong></dt>
<dd><p>A C string constant for text to be output after each <code>asm</code>
statement or group of consecutive ones.  Normally this is
<code>&quot;#NO_APP&quot;</code>, which tells the GNU assembler to resume making the
time-saving assumptions that are valid for ordinary compiler output.
</p></dd></dl>

<dl>
<dt><a name="index-ASM_005fOUTPUT_005fSOURCE_005fFILENAME"></a>Macro: <strong>ASM_OUTPUT_SOURCE_FILENAME</strong> <em>(<var>stream</var>, <var>name</var>)</em></dt>
<dd><p>A C statement to output COFF information or DWARF debugging information
which indicates that filename <var>name</var> is the current source file to
the stdio stream <var>stream</var>.
</p>
<p>This macro need not be defined if the standard form of output
for the file format in use is appropriate.
</p></dd></dl>

<dl>
<dt><a name="index-TARGET_005fASM_005fOUTPUT_005fSOURCE_005fFILENAME"></a>Target Hook: <em>void</em> <strong>TARGET_ASM_OUTPUT_SOURCE_FILENAME</strong> <em>(FILE *<var>file</var>, const char *<var>name</var>)</em></dt>
<dd><p>Output DWARF debugging information which indicates that filename
<var>name</var> is the current source file to the stdio stream <var>file</var>.
</p>
<p>This target hook need not be defined if the standard form of output
for the file format in use is appropriate.
</p></dd></dl>

<dl>
<dt><a name="index-TARGET_005fASM_005fOUTPUT_005fIDENT"></a>Target Hook: <em>void</em> <strong>TARGET_ASM_OUTPUT_IDENT</strong> <em>(const char *<var>name</var>)</em></dt>
<dd><p>Output a string based on <var>name</var>, suitable for the &lsquo;<samp>#ident</samp>&rsquo;
directive, or the equivalent directive or pragma in non-C-family languages.
If this hook is not defined, nothing is output for the &lsquo;<samp>#ident</samp>&rsquo;
directive.
</p></dd></dl>

<dl>
<dt><a name="index-OUTPUT_005fQUOTED_005fSTRING"></a>Macro: <strong>OUTPUT_QUOTED_STRING</strong> <em>(<var>stream</var>, <var>string</var>)</em></dt>
<dd><p>A C statement to output the string <var>string</var> to the stdio stream
<var>stream</var>.  If you do not call the function <code>output_quoted_string</code>
in your config files, GCC will only call it to output filenames to
the assembler source.  So you can use it to canonicalize the format
of the filename using this macro.
</p></dd></dl>

<dl>
<dt><a name="index-TARGET_005fASM_005fNAMED_005fSECTION"></a>Target Hook: <em>void</em> <strong>TARGET_ASM_NAMED_SECTION</strong> <em>(const char *<var>name</var>, unsigned int <var>flags</var>, tree <var>decl</var>)</em></dt>
<dd><p>Output assembly directives to switch to section <var>name</var>.  The section
should have attributes as specified by <var>flags</var>, which is a bit mask
of the <code>SECTION_*</code> flags defined in <samp>output.h</samp>.  If <var>decl</var>
is non-NULL, it is the <code>VAR_DECL</code> or <code>FUNCTION_DECL</code> with which
this section is associated.
</p></dd></dl>

<dl>
<dt><a name="index-TARGET_005fASM_005fELF_005fFLAGS_005fNUMERIC"></a>Target Hook: <em>bool</em> <strong>TARGET_ASM_ELF_FLAGS_NUMERIC</strong> <em>(unsigned int <var>flags</var>, unsigned int *<var>num</var>)</em></dt>
<dd><p>This hook can be used to encode ELF section flags for which no letter
code has been defined in the assembler.  It is called by
<code>default_asm_named_section</code> whenever the section flags need to be
emitted in the assembler output.  If the hook returns true, then the
numerical value for ELF section flags should be calculated from
<var>flags</var> and saved in <var>*num</var>; the value is printed out instead of the
normal sequence of letter codes.  If the hook is not defined, or if it
returns false, then <var>num</var> is ignored and the traditional letter sequence
is emitted.
</p></dd></dl>

<dl>
<dt><a name="index-TARGET_005fASM_005fFUNCTION_005fSECTION"></a>Target Hook: <em>section *</em> <strong>TARGET_ASM_FUNCTION_SECTION</strong> <em>(tree <var>decl</var>, enum node_frequency <var>freq</var>, bool <var>startup</var>, bool <var>exit</var>)</em></dt>
<dd><p>Return preferred text (sub)section for function <var>decl</var>.
Main purpose of this function is to separate cold, normal and hot
functions. <var>startup</var> is true when function is known to be used only
at startup (from static constructors or it is <code>main()</code>).
<var>exit</var> is true when function is known to be used only at exit
(from static destructors).
Return NULL if function should go to default text section.
</p></dd></dl>

<dl>
<dt><a name="index-TARGET_005fASM_005fFUNCTION_005fSWITCHED_005fTEXT_005fSECTIONS"></a>Target Hook: <em>void</em> <strong>TARGET_ASM_FUNCTION_SWITCHED_TEXT_SECTIONS</strong> <em>(FILE *<var>file</var>, tree <var>decl</var>, bool <var>new_is_cold</var>)</em></dt>
<dd><p>Used by the target to emit any assembler directives or additional
labels needed when a function is partitioned between different
sections.  Output should be written to <var>file</var>.  The function
decl is available as <var>decl</var> and the new section is &lsquo;cold&rsquo; if
<var>new_is_cold</var> is <code>true</code>.
</p></dd></dl>

<dl>
<dt><a name="index-TARGET_005fHAVE_005fNAMED_005fSECTIONS"></a>Common Target Hook: <em>bool</em> <strong>TARGET_HAVE_NAMED_SECTIONS</strong></dt>
<dd><p>This flag is true if the target supports <code>TARGET_ASM_NAMED_SECTION</code>.
It must not be modified by command-line option processing.
</p></dd></dl>

<a name="TARGET_005fHAVE_005fSWITCHABLE_005fBSS_005fSECTIONS"></a><dl>
<dt><a name="index-TARGET_005fHAVE_005fSWITCHABLE_005fBSS_005fSECTIONS"></a>Target Hook: <em>bool</em> <strong>TARGET_HAVE_SWITCHABLE_BSS_SECTIONS</strong></dt>
<dd><p>This flag is true if we can create zeroed data by switching to a BSS
section and then using <code>ASM_OUTPUT_SKIP</code> to allocate the space.
This is true on most ELF targets.
</p></dd></dl>

<dl>
<dt><a name="index-TARGET_005fSECTION_005fTYPE_005fFLAGS"></a>Target Hook: <em>unsigned int</em> <strong>TARGET_SECTION_TYPE_FLAGS</strong> <em>(tree <var>decl</var>, const char *<var>name</var>, int <var>reloc</var>)</em></dt>
<dd><p>Choose a set of section attributes for use by <code>TARGET_ASM_NAMED_SECTION</code>
based on a variable or function decl, a section name, and whether or not the
declaration&rsquo;s initializer may contain runtime relocations.  <var>decl</var> may be
null, in which case read-write data should be assumed.
</p>
<p>The default version of this function handles choosing code vs data,
read-only vs read-write data, and <code>flag_pic</code>.  You should only
need to override this if your target has special flags that might be
set via <code>__attribute__</code>.
</p></dd></dl>

<dl>
<dt><a name="index-TARGET_005fASM_005fRECORD_005fGCC_005fSWITCHES"></a>Target Hook: <em>void</em> <strong>TARGET_ASM_RECORD_GCC_SWITCHES</strong> <em>(const char *<var></var>)</em></dt>
<dd><p>Provides the target with the ability to record the gcc command line
switches provided as argument.
</p>
<p>By default this hook is set to NULL, but an example implementation is
provided for ELF based targets.  Called <var>elf_record_gcc_switches</var>,
it records the switches as ASCII text inside a new, string mergeable
section in the assembler output file.  The name of the new section is
provided by the <code>TARGET_ASM_RECORD_GCC_SWITCHES_SECTION</code> target
hook.
</p></dd></dl>

<dl>
<dt><a name="index-TARGET_005fASM_005fRECORD_005fGCC_005fSWITCHES_005fSECTION"></a>Target Hook: <em>const char *</em> <strong>TARGET_ASM_RECORD_GCC_SWITCHES_SECTION</strong></dt>
<dd><p>This is the name of the section that will be created by the example
ELF implementation of the <code>TARGET_ASM_RECORD_GCC_SWITCHES</code> target
hook.
</p></dd></dl>

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